1. Field of the Invention
The present invention relates to probe cards for probing devices under test and more particularly, to a high frequency probe card for probing a photoelectric device.
2. Description of the Related Art
In a task of testing semiconductor chip, the tester is indirectly and electrically connected with a device under test (hereinafter referred to as ‘DUT’) through a probe card. The conventional probe card is generally composed of a circuit board and a plurality of probes. On the top surface of the circuit board, a plurality of top contact pads for being electrically contacted by the tester are provided. The bottom surface of the circuit board is provided with bottom contact pads electrically connected with the top contact pads. The probes are respectively soldered to the bottom contact pads and arranged in a pattern corresponding to that of contacts of the DUT. When the probes contact the corresponding contacts of the DUT respectively, they can transmit the testing signals from the tester to the DUT for enabling the tester to detect and measure the electric characteristics of the DUT.
The probe card designed for testing image sensing devices, such as CMOS image sensors, or other photoelectric devices further comprises an opening in which a lens module is mounted. When the probe card probes the DUT, testing light can reach on the DUT through the lens module. After the DUT receives the testing light, the DUT converts the testing light to electric signal, which is transmitted to the tester through the probe card for enabling the tester to analyze characteristics of the DUT.
Nowadays, the lens modules used in electronic devices usually have a smaller size with a larger numbers of pixels; therefore, the photoelectric device usually works under a high frequency condition. In order to transmit the high frequency testing signals effectively, the probe card must have a certain impedance matching with those of the tester and the DUT so as to accurately reflect the test result. However, the commercially available probe cards for probing photoelectric devices cannot fulfill the requirement of high frequency testing at present.
In another aspect, the top contact pads of the circuit board of the probe card are electrically connected with the bottom contact pads through an internal circuit layout of the circuit board. Therefore, it is difficult in manufacturing such a circuit board, and the signals may not be smoothly transmitted due to the fact that the internal circuit layout may have many bends and curves. Further, if the internal circuit layout of the circuit board is configured having a high frequency signal trace accompanying a grounding trace for impedance matching, the circuit board will be more difficultly manufactured.